Polishing head and edge control ring thereof, and method of increasing polishing rate at wafer edge

ABSTRACT

A polishing head used for CMP is described, including a retaining ring that is for engaging with a wafer, a membrane and an edge control ring. The membrane includes a bottom part for engaging with the wafer, and a lip part contiguous with the bottom part. The edge control ring is disposed between the retaining ring and the membrane, including a bottom part that has an abutting surface. The abutting surface of the edge control ring contacts with the external surface of the lip part of the membrane when the membrane is not inflated.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to equipment used in semiconductor processes, and more particularly to a polishing head used for CMP, an edge control ring to be mounted on a polishing head and a method of increasing the polishing rate at the edge of a wafer.

2. Description of Related Art

Chemical mechanical polishing (CMP) is currently a technique widely used for global planarization. In a typical CMP process, a wafer is held by a polishing head with the surface to be polished facing down and pressed onto a rotating polishing pad usually supplied with a polishing slurry. With a relative movement between the wafer and the pad, the wafer surface is planarized by chemical and mechanical effects.

Along with the evolution of IC process, various modified or new CMP methods have been provided. Except the polishing pad and slurry that have been much studied, the polishing head has also been provided with some modifications and improvements.

FIG. 1 depicts a type of polishing head in the prior art. The polishing head 100 includes a flexible membrane 110, an edge control ring 150 and a retaining ring 190. The retaining ring 190 is for retaining the wafer 10 under the mounting surface 112 a of the membrane 110. The edge control ring 150 is disposed between the membrane 110 and the retaining ring 190. The inner surface of the edge control ring 150 engages with the column part 116 of the membrane 110, but the bottom surface 154 of the former is separated from the lip part 114 of the latter by a gap 130. The mounting surface 112 a of the bottom part 112 of the membrane 110 can engage with a wafer 10, and the load thereon is controlled by increasing/decreasing the gas pressure in the chamber (not shown) behind the membrane 110.

However, when the above polishing head is used in CMP, the polishing rate at the wafer edge is insufficient so that residue of the target layer is present at the wafer edge and may cause circuit short that lowers the product yield.

To solve the above residue problem, U.S. Pat. Nos. 6,979,250 and 6,776,694 provide some new polishing heads, which however still cannot effectively improve the polishing rate at the wafer edge and solve the residue problem. The main reason is that a gap is present between the bottom surface of the edge control ring and the external surface of the lip part of the membrane to cause lift of the lip part as the membrane is inflated. The lift lowers or vanishes the load that the lip part applies to the wafer edge so that the polishing rate at the wafer edge is insufficient.

SUMMARY OF THE INVENTION

Accordingly, this invention provides a polishing head used for CMP, which can solve the problem that the target layer at the wafer edge cannot be polished effectively.

This invention also provides an edge control ring to be mounted on a polishing head used for CMP, which can solve the above problem.

This invention further provides a method of increasing the polishing rate at the wafer edge in a CMP process using a polishing head.

The polishing head of this invention includes a retaining ring for engaging with a wafer, a membrane and an edge control ring. The membrane includes a bottom part and a lip part contiguous with the bottom part, wherein the bottom part is for engaging with the wafer. The edge control ring is disposed between the retaining ring and the membrane, and includes a bottom part that has an abutting surface. The abutting surface of the edge control ring contacts with the external surface of the lip part when the membrane is not inflated.

In an embodiment, the abutting surface of the edge control ring and the external surface of the lip part are inclined surfaces. The bottom part of the edge control ring may have at least one recess therein, which may be a point recess or groove. As the at least one recess is a groove, an O-ring may be disposed in the same. The edge control ring may be a composite of at least two rings, which may include different materials. The two rings may include an upper ring and a lower ring, or an inner ring and an outer ring. Moreover, the edge control ring may have a height adjusting mechanism thereon. The edge control ring can be formed in an integral. The abutting surface of the edge control ring may extend to above the edge of the lip part of the membrane.

In an embodiment, the abutting surface of the edge control ring and the external surface of the lip part are horizontal surfaces.

In an embodiment, the internal surface of the lip part of the membrane is an inclined surface, and there is a gap between the internal surface of the lip part and the bottom part of the membrane.

In an embodiment, the lip part of the membrane is a solid part and there is no gap between the lip part and the bottom part of the membrane.

In an embodiment, the lip part includes a material different from that of the rest of the membrane. For example, the lip part may include a more rigid material.

The edge control ring of this invention includes an inner surface, an outer surface and a bottom part between them which has an inclined abutting surface. The inclined abutting surface contacts with the lip part when the membrane is not inflated.

In an embodiment, the edge control ring further includes an extension part on the inner surface thereof to engage with the membrane.

In an embodiment, the bottom part of the edge control ring has at least one recess therein, which may be a point recess or a groove. As the at least one recess is a groove, the edge control ring may further include an O-ring in the groove.

In an embodiment, the edge control ring is a composite of at least two rings that may include different materials. The at least two rings may include an upper ring and a lower ring or alternatively include an inner ring and an outer ring.

In an embodiment, the edge control ring is formed in an integral.

In an embodiment, the edge control ring may further have a height adjusting mechanism thereon.

The method of increasing the polishing rate at the wafer edge of this invention includes fabricating the edge control ring and the membrane in a manner such that the abutting surface of the bottom part of the edge control ring contacts with the external surface of the lip part when the membrane is not inflated.

In an embodiment, the abutting surface of the edge control ring and the external surface of the lip part are inclined surfaces.

In an embodiment, the abutting surface of the edge control ring and the external surface of the lip part are horizontal surfaces.

In an embodiment, the abutting surface of the edge control ring extends to above the edge of the lip part of the membrane.

In an embodiment, the weight of the lip part is increased to increase the load on the wafer edge. This may be done by forming the lip part as a solid part or by forming the same from a material having a density higher than that of the rest of the membrane.

In an embodiment, the edge control ring also has a height adjusting mechanism thereon, and the method further includes using the height adjusting mechanism to adjust the height of the edge control ring and thereby increase the load on the wafer edge.

In an embodiment, the bottom part of the edge control ring has a groove therein, and the edge control ring further includes an O-ring in the groove.

Since the abutting surface of the edge control ring contacts with the external surface of the lip part of the membrane as the membrane is not inflated, the lip part cannot lift as the membrane is inflated so that the load on the wafer edge applied by the lip part is larger than that in the prior art as the membrane is inflated. Thereby, the polishing rate at the wafer edge is increased and the edge residue problem is solved.

In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross section of a conventional type of polishing head.

FIG. 2 depicts a cross section of a non-inflated polishing head according to an embodiment of this invention.

FIG. 3 depicts a cross section of a non-inflated polishing head according to another embodiment of this invention.

FIG. 4 depicts a cross section of a non-inflated polishing head according to still another embodiment of this invention.

FIGS. 5A and 5B depict cross sections of two non-inflated polishing heads according to still another embodiment of this invention, wherein the edge control ring is a composite of two rings.

FIG. 6 depicts a cross section of a non-inflated polishing head according to still another embodiment of this invention, wherein the edge control ring has two flat abutting surfaces having different inclination angles at its bottom.

FIGS. 7A-7E depict cross sections of five non-inflated polishing heads according to still another embodiment of this invention, wherein the edge control rings of the polishing heads have recesses of different shapes at their bottoms.

FIG. 8 depicts a cross section of a non-inflated polishing head according to still another embodiment of this invention, wherein the bottom part of the edge control ring has grooves therein and includes O-rings in the grooves.

FIG. 9 depicts a cross section of a non-inflated polishing head according to still another embodiment of this invention, wherein the edge control ring has a height adjusting mechanism thereon.

FIGS. 10, 11A, 11B, 12A and 12B depict cross sections of five non-inflated polishing heads according to still another embodiment of this invention, wherein the lip part of the membrane is a solid part.

FIG. 13 shows a cross section of a non-inflated polishing head according to still another embodiment of this invention, wherein the lip part of the membrane is made from a material different form that of the rest of the membrane.

FIGS. 14A and 14B depict cross sections of two non-inflated polishing heads according to still another embodiment of this invention, wherein the external surfaces of the lip parts of the membranes thereof have therein recesses of different shapes.

DESCRIPTION OF EMBODIMENTS

This invention is based on that the abutting surface of the edge control ring contacts with the lip part of the membrane when the membrane is not inflated, which prevent lift of the lip part so that the lip part applies a sufficient pressure to the wafer edge after the membrane is inflated. The following embodiments describe exemplary modifications to the edge control ring and/or the membrane under the above limitation.

FIG. 2 depicts a cross section of a non-inflated polishing head according to an embodiment of this invention.

Referring to FIG. 2, the polishing head 200 includes a flexible membrane 210, an edge control ring 250 and a retaining ring 290. Other members of the polishing head 200 can be found in U.S. Pat. No. 6,979,250 or 6,776,694 and are omitted in FIG. 2. The retaining ring 290 usually has an annular shape and is fixed at the periphery of the main part (not shown) of the polishing head 200. When fluid is pump into the load chamber (not shown) in the polishing head 200 to push the main part down, the retaining ring 290 is also pushed down to press the polishing pad. The internal surface of the retaining ring 290 can restrict the movement of the wafer 20 to retain the same under the bottom surface 212 of the membrane 210.

The membrane 210 is disposed over the wafer 200, including a bottom part 212, a lip part 214, a column part 216 and a wing part 218 that are contiguous in sequence. The bottom surface 212 a of the bottom part 212 extends to the edge of the wafer 20 for engaging with the whole surface of the wafer 20. The lip part 214 is an inclined part extending from the external surface 222 of the column part 216 to the bottom part 212. The wing part 218 extends to above the edge control ring 250 and the retaining ring 290. The load on the wafer 20 can be adjusted by increasing and decreasing the gas pressure in the chamber behind the membrane 210.

The edge control ring 250 is disposed between the membrane 210 and the retaining ring 290 and extends down to contact with the lip part 214 of the membrane 210. That is, the height of the edge control ring 250 is increased to L2 from L1 of the prior art. More specifically, the edge control ring 250 includes an inner surface 252, an outer surface 258, a bottom part 254 and an extension part 260. The inner surface 252 is engaged with the column part 216 of the membrane 210, and the extension part 260 of the former is engaged between the column part 216 and the wing part 218 of the latter. The bottom part 254 of the edge control ring 250 is an inclined part between the inner surface 252 and the outer surface 258 of the same that has an inclined abutting surface 254 a. When the membrane 210 is not inflated, the inclined abutting surface 254 a contacts with the external surface 214 a of the lip part 214 of the membrane 210.

The above method for solving the edge residue problem is to extend the edge control ring down to prevent lift of the lip part of the membrane, wherein the structure of the membrane is unchanged. Since only the structure of the edge control ring has to be modified and an edge control ring can be easily and rapidly fabricated at a low cost, the method is cheap and effective in solving the edge residue problem.

Though it is the bottom part of the edge control ring that is modified to match the inclined external surface of the lip part of the membrane in the above case, it is alternatively possible to maintain the horizontal abutting surface of the edge control ring but modify the shape of the lip part of the membrane such that the abutting surface contacts with the lip part when the membrane is not inflated.

FIG. 3 depicts a cross section of a non-inflated polishing head according to another embodiment of this invention.

Referring to FIG. 3, the polishing head 300 is similar to the polishing head 200 in FIG. 2 in the structure except the structures of the lip part 314 of the membrane 310 and the bottom part 354 of the edge control ring 350. The unchanged parts in FIG. 3 are indicated by the same reference characters and are not described again.

In the polishing head 300, the edge control ring 350 is between the membrane 310 and the retaining ring 290 and similarly extends down to contact with the lip part 314 of the membrane 310 as having a height “L3”. However, both the bottom abutting surface 354 a of the bottom part 354 of the edge control ring 350 and the external surface 314 a of the lip part 314 of the membrane 310 are changed to horizontal surfaces so that the former contacts with the latter when the membrane 310 is not inflated.

The above method of solving the edge residue problem is to modify the structure of the membrane and extend the edge control ring down to prevent lift of the lip part of the membrane. However, it is also possible to keep the structure of the edge control ring in the prior art but modify that of the membrane to prevent lift of the lip part.

FIG. 4 depicts a cross section of a non-inflated polishing head according to still another embodiment of this invention.

Referring to FIG. 4, the polishing head 400 is similar to the polishing head 300 in FIG. 3 in the structure except the structure of the lip part 414 of the membrane 410 and the height (L4) of the edge control ring 450. The unchanged parts in FIG. 4 are indicated by the same reference characters and are not described again.

The edge control ring 450 is similar to a conventional one in the height and the shape. To compensate the insufficient vertical dimension of the edge control ring 450, the lip part 414 of the membrane 410 is shifted upward to contact with the edge control ring 450. The lip part 414 of the membrane 410 still connects between the column part 216 and the bottom part 212 of the same, but instead extends horizontally from above the bottom end 222 a of the external surface 222 of the column part 216 to the bottom part 212 of the same with its external surface 414 a contacting with the bottom abutting surface 454 a of the edge control ring 450. Accordingly, the external surface 414 a of the lip part 414 of the membrane 410 is changed to a horizontal surface to match the horizontal abutting surface 454 a of the edge control ring 450.

The edge control ring in each of the above three embodiments may be fabricated in an integral from, for example, a steel material like stainless steel, but the edge control ring of this invention may alternatively be fabricated as a composite of at least two rings. Two such examples where the abutting surfaces of the bottom part of the edge control ring and the lip part of the membrane are inclined surfaces are provide below, but the embodiment is not limited to such a design.

FIGS. 5A-5B depict cross sections of two non-inflated polishing heads according to still another embodiment, wherein the edge control ring is a composite of two rings.

Referring to FIG. 5A, the edge control ring 250 is fabricated by combining an upper ring 250 a and a lower ring 250 b, which may include the same material or include different materials. It is preferred that the upper ring 250 a includes a relatively rigid material and the lower ring 250 b includes a relatively elastic material, so as to facilitate the adjustment of the pressure to the wafer. The respective heights of the upper ring 250 a and the lower ring 250 b are not particularly limited and can be adjusted as required. Referring to FIG. 5B, the edge control ring 250 is fabricated by combining an inner ring 250 c and an outer ring 250 d, which may include the same material or include different materials to facilitate the adjustment of the pressure to the wafer. The respective thicknesses of the inner ring 250 c and the outer ring 250 d are not particularly limited and can be adjusted as required. Though the edge control ring is fabricated by combining two rings in the above examples, the edge control ring of this embodiment may alternatively be fabricated by combining more than two rings.

The abutting surface 254 a, 354 a or 454 a of the bottom part 254, 354 or 454 of the edge control ring 250, 350 or 450 in FIG. 2, 3 or 4 is a flat surface having only one (inclination) angle that entirely contacts with the lip part 214 of the membrane 210. However, the edge control ring of this invention is not limited to have the above feature. The bottom part 254, 354 or 454 of the edge control ring 250, 350 or 450 may have two or more flat abutting surfaces having different (inclination) angles. One such example where the abutting surfaces of the edge control ring and the lip part of the membrane are inclined surfaces is provide below, but the embodiment is not limited to such a design.

Referring to FIG. 6, the bottom part 254 of the edge control ring 250 have two flat abutting surfaces 254 b and 254 c, wherein the surface 254 b is more inclined than the surface 254 c, so that the surface 254 c pushes the lip part 214 closer to the wafer edge to increase the load on the wafer edge.

Moreover, the bottom part 254, 354 or 454 of the edge control ring 250, 350 or 450 in FIG. 2, 3 or 4 is not limited to have a flat surface but may alternatively have at least one recess therein. Some such example where the abutting surfaces of the bottom part of the edge control ring and the lip part of the membrane are inclined surfaces are provide below, but the embodiment is not limited to such a design.

FIGS. 7A-7E depict cross sections of five non-inflated polishing heads according to still another embodiment of this invention, wherein the edge control ring of each polishing head has at least one recess at its bottom. The at least one recess can be a point recess or a circumferential groove in the edge control ring 250. When the at least one recess is a point recess, it may be a rectangular-cornered recess 271 as shown in FIG. 7A, a round-cornered recess 274 as shown in FIG. 7D, a V-shaped recess 272 as shown in FIG. 7B, or a point recess of any other possible shape.

In the descriptions for FIG. 7A-7E, a “recess” means a circumferential groove in the bottom part of the edge control ring 250. However, a recess in the bottom part of the edge control ring is not limited to be a circumferential groove in this embodiment.

Referring to FIG. 7A, the bottom part 254 of the edge control ring 250 has some rectangular-cornered recesses 271 therein dividing the abutting surface 271 a contacting with the lip part 214 of the membrane 210. Referring to FIG. 7B, the bottom part 254 has some separated V-shaped recesses 272 therein that divide the abutting surface 272 a contacting with the lip part 214. Referring to FIG. 7C, the bottom part 254 has some adjoining V-shaped recesses 273 therein and thereby has a zigzag-shaped profile in the cross-sectional view, while the apexes between the V-shaped recesses 273 constitute an abutting surface 273 a contacting with the lip part 214. Referring to FIG. 7D, the bottom part 254 has separated round-cornered recesses 274 therein dividing the abutting surface 274 a contacting with the lip part 214. Referring to FIG. 7E, the bottom part 254 has some adjoining round-cornered recesses 275 therein, while the apexes between the recesses 275 constitute an abutting surface 275 a contacting with the lip part 214.

The shape of the recess in the bottom part of the edge control ring is not limited to the above-mentioned and may have any possible variation. For example, when the bottom part of the edge control ring has two or more recesses therein, the recesses may have two or more different shapes as mentioned above, or include point and groove-like recesses at the same time. Moreover, a ring of an elastic material can be further mounted in a groove-like recess 271, 272, 273, 274 or 275 in the FIG. 7A, 7B, 7C, 7D or 7E. For example, as shown in FIG. 8, an O-ring 280 can be mounted in each of the separated round-cornered groove-like recesses 274 in FIG. 7D. The material of the O-ring 280 may be rubber. The O-ring 280 can help pushing the lip part 214 of the membrane 210 to increase the load on the wafer edge and the polishing rate thereat.

Except the above modifications in the structure, the edge control ring may have a certain mechanism thereon, which is possibly a height adjusting mechanism. One such example where the edge control ring includes separated upper and lower rings and the abutting surfaces of the edge control ring and the lip part of the membrane are inclined surfaces is provide below, but the embodiment is not limited to such a design.

Referring to FIG. 9, the edge control ring 250 has a height adjusting mechanism 240 thereon, which possibly includes screws 241 between the upper ring 250 a and the lower ring 250 b and corresponding screw holes in the two rings 250 a and 250 b. By screwing the screw 241, the height of the edge control ring 250 can be increased to increase the load on a wafer edge and the polishing rate thereat.

On the other hand, it is also possible to increase the polishing rate at the wafer edge by modifying the structure of the membrane.

The lip part 214, 314 or 414 of the membrane 210, 310 or 410 in FIG. 2, 3 or 4 is merely a thin film that is partially separated from the bottom part 212 by a gap, but the lip part of the membrane may alternatively be a solid part that is entirely contiguous with or partially separated from the bottom part to increase the weight of the lip part and thereby increase the load on the wafer edge and the polishing rate thereat. Such examples are shown in FIGS. 10, 11A-11B and 12A-12B, respectively derived from the structures shown in FIGS. 2, 3 and 4 respectively. However, the polishing head of the embodiment is not limited to the examples.

Referring to FIG. 10, the lip part 294 of the membrane 210 is a solid part. The external surface 294 a of the lip part 294 and the bottom abutting surface 254 a of the edge control 250 are inclined surfaces.

Referring to FIG. 11A, the lip part 394 of the membrane 310 is a solid part with a rectangular cross section. The external surface 394 a of the lip part 394 and the bottom abutting surface 354 a of the edge control 350 are horizontal surfaces.

Referring to FIG. 11B, the lip part 395 of the membrane 310 is a solid part. The external surface 395 a of the lip part 395 and the bottom abutting surface 354 a of the edge control 350 are horizontal, but the internal surface 395 b of the former is inclined and is apart from the bottom part 212 of the membrane 310 by a gap.

Referring to FIG. 12A, the lip part 494 of the membrane 410 is a thickened solid part with a rectangular cross section. The external surface 494 a of the lip part 394 and the bottom abutting surface 454 a of the edge control 450 are horizontal surfaces.

Referring to FIG. 12B, the lip part 495 of the membrane 410 is a thickened solid part. The external surface 495 a of the lip part 495 and the abutting surface 454 a of the edge control 450 are horizontal surfaces, but the internal surface 495 b of the former is an inclined surface apart from the bottom part 212 of the membrane 410 by a gap.

Moreover, the membrane in the polishing head of this invention may be made from a single material or from two or more materials. Taking the structure in FIG. 10 as an example, the lip part 294 of the membrane 210 may be made from a material different from that of the rest of the same, as shown in FIG. 13, so as to increase the load on the wafer edge. The material of the lip part 294 of the membrane 210 may have a density or rigidity higher than that of the material of the rest of the same.

Furthermore, the external surface of the lip part of the membrane may also have at least one recess therein as in the case of the edge control ring. Such examples are shown in FIGS. 14A and 14B, respectively derived from the structures in FIGS. 2 and 10. However, the polishing head of this embodiment is not limited to the examples.

Referring to FIG. 14A/B, the external surface 214 a/294 a of the lip part 214/294 of the membrane 210 have recesses 215 therein. Each recess 215 may be a point recess or a groove and may be further modified as in the case of the structures in FIGS. 7A-7E. It is noted that only recesses as rectangular-cornered grooves are shown in FIGS. 14A and 14B; other possible shape for a recess can be seen in FIGS. 7B-7E.

It is noted that the above embodiments merely describe certain combinations of the aforementioned modifications to the edge control ring and/or the membrane. Other combinations of the aforementioned modifications to the edge control ring and/or the membrane are also possible as required, if only the bottom part of the edge control ring contacts with the lip part of the membrane when the membrane is not inflated.

Since the abutting surface of the edge control ring contacts with the lip part of the membrane when the latter is not inflated, the lip part cannot lift after the membrane is inflated, so that the load on the wafer edge caused by the lip part is larger than that in the prior art after the membrane is inflated. Thereby, the polishing rate at the wafer edge is increased and the edge residue problem is solved.

This invention has been disclosed above in the preferred embodiments, but is not limited to those. It is known to persons skilled in the art that some modifications and innovations may be made without departing from the spirit and scope of this invention. Hence, the scope of this invention should be defined by the following claims. 

1. A polishing head used for chemical mechanical polishing (CMP), comprising: a retaining ring for engaging with a wafer; a membrane, including a bottom part and a lip part contiguous with the bottom part, wherein the bottom part is for engaging with the wafer; and an edge control ring between the retaining ring and the membrane, which includes a bottom part having an abutting surface, wherein the abutting surface of the edge control ring contacts with an external surface of the lip part when the membrane is not inflated.
 2. The polishing head of claim 1, wherein the abutting surface of the edge control ring and the external surface of the lip part are inclined surfaces.
 3. The polishing head of claim 2, wherein the bottom part of the edge control ring has at least one recess therein.
 4. The polishing head of claim 3, wherein the at least one recess comprises a point recess or a groove.
 5. The polishing head of claim 4, wherein the at least one recess comprises a groove and the edge control ring further comprises an O-ring in the groove.
 6. The polishing head of claim 2, wherein the edge control ring is a composite of at least two rings.
 7. The polishing head of claim 6, wherein the at least two rings comprise different materials.
 8. The polishing head of claim 6, wherein the at least two rings comprise an upper ring and a lower ring or comprise an inner ring and an outer ring.
 9. The polishing head of claim 2, wherein the edge control ring has a height adjusting mechanism thereon.
 10. The polishing head of claim 2, wherein the edge control ring is formed in an integral.
 11. The polishing head of claim 2, wherein the abutting surface of the edge control ring extends to above an edge of the lip part.
 12. The polishing head of claim 1, wherein the abutting surface of the edge control ring and the external surface of the lip part are horizontal surfaces.
 13. The polishing head of claim 1, wherein an internal surface of the lip part of the membrane is an inclined surface, and there is a gap between the internal surface of the lip part of the membrane and the bottom part of the membrane.
 14. The polishing head of claim 1, wherein the lip part is a solid part, and there is no gap between the lip part and the bottom part of the membrane.
 15. The polishing head of claim 1, wherein the lip part of the membrane comprises a material different from a material of the rest of the membrane.
 16. The polishing head of claim 15, wherein the lip part of the membrane comprises a material more rigid than a material of the rest of the membrane.
 17. An edge control ring that is to be mounted on a polishing head used for CMP, wherein the polishing head also comprises a membrane that has a lip part under the edge control ring and is inflated in a CMP process, the edge control ring comprising: an inner surface, an outer surface and a bottom part between them which has an inclined abutting surface, wherein the inclined abutting surface contacts with the lip part of the membrane when the membrane is not inflated.
 18. The edge control ring of claim 17, further comprising an extension part on the inner surface thereof to engage with the membrane.
 19. The edge control ring of claim 17, wherein the bottom part has at least one recess therein.
 20. The edge control ring of claim 19, wherein the at least one recess comprises a point recess or a groove.
 21. The edge control ring of claim 20, wherein the at least one recess comprises a point recess, further comprising an O-ring in the groove.
 22. The edge control ring of claim 17, which is a composite of at least two rings.
 23. The edge control ring of claim 22, wherein the at least two rings comprise different materials.
 24. The edge control ring of claim 22, wherein the at least two rings comprise an upper ring and a lower ring or comprise an inner ring and an outer ring.
 25. The edge control ring of claim 17, which is formed in an integral.
 26. The edge control ring of claim 17, further having a height adjusting mechanism thereon.
 27. A method of increasing a polishing rate at a wafer edge in a CMP process that uses a polishing head, the polishing head comprising an edge control ring and a membrane that has a lip part under the edge control ring and is inflated in the CMP process, the method comprising: fabricating the edge control ring and the membrane in a manner such that an abutting surface of a bottom part of the edge control ring contacts with an external surface of the lip part of the membrane when the membrane is not inflated.
 28. The method of claim 27, wherein the abutting surface of the edge control ring and the external surface of the lip part of the membrane are inclined surfaces.
 29. The method of claim 27, wherein the abutting surface of the edge control ring and the external surface of the lip part of the membrane are horizontal surfaces.
 30. The method of claim 27, wherein the abutting surface of the edge control ring extends to above an edge of the lip part of the membrane.
 31. The method of claim 27, further comprising increasing a weight of the lip part of the membrane to increase a load on the wafer edge.
 32. The method of claim 31, wherein increasing the weight of the lip part of the membrane comprises forming the lip part as a solid part.
 33. The method of claim 31, wherein increasing the weight of the lip part of the membrane comprises forming the lip part from a material that has a density higher than a density of a material of the rest of the membrane.
 34. The method of claim 27, wherein the edge control ring has a height adjusting mechanism thereon, further comprising using the height adjusting mechanism to adjust a height of the edge control ring and thereby increase a load on the wafer edge.
 35. The method of claim 27, wherein the bottom part of the edge control ring has a groove therein and the edge control ring further comprises an O-ring in the groove. 